The central goal is to develop a better understanding of the factors and elements which control functional behavior of the human hemoglobin molecule. The approach that will be employed is to identify the roles of amino acid side chains in the molecule's normal functioning by residue substitution at specifically targeted sites coupled with extensive structural and functional characterization of the resulting hemoglobin molecules. This Program Project brings together seven research groups that have complementary areas of expertise and a common focus of interest on mechanisms of hemoglobin function and structure. In order to achieve this concentrated effort, it has been necessary to bring together individuals from a number of different institutions. (We know of no single institution with a comparable level of interest and expertise in this field.) This group has a proven track record of productive collaboration during the previous period of this grant. Other strengths include: a) efficiently functioning core facilities that have been developed under the current funding of this Program Project for production of large amounts of genetically engineered hemoglobin variants. b) Facilities and expertise for detailed, systematic characterization of structural (i.e., x-ray, spectroscopic, and theoretical) and functional (kinetic and thermodynamic) properties of hemoglobin. Work in the different laboratories will be coordinated through planned collaborations, exchanges of materials and personnel, and quarterly meetings. Results will be synthesized into a predictive model of the hemoglobin mechanism. This new level of understanding may permit the rational design of structurally-modified hemoglobins with desired properties, including potential red cell substitute materials.